Multiple-input multiple-output (MIMO) technology brings a revolutionary change to wireless communications. With deployment of a plurality of antennas on a transmit-end device and a receive-end device, the MIMO technology can significantly improve performance of a wireless communications system. For example, in a diversity scenario, the MIMO technology can improve transmission reliability effectively, and in a multiplexing scenario, the MIMO technology can increase a transmission throughput greatly.
A MIMO system usually uses a precoding technology to improve a channel, so as to improve an effect of spatial multiplexing. Specifically, in the precoding technology, a precoding matrix that matches a channel is used to process a data stream for spatial multiplexing (spatial stream for short), so as to precode the channel and improve reception quality of the spatial stream.
Each spatial stream that participates in spatial multiplexing corresponds to one column vector of a precoding matrix. In the precoding process, the transmit-end device uses the column vector to precode the spatial stream. Therefore, the column vector may also be referred to as a precoding vector. The precoding vector may be determined by the receive-end device based on a basic codebook, and fed back to the transmit-end device. The basic codebook is a set of candidate vectors, and a weighted sum of a plurality of candidate vectors that match a channel the most can be used as the precoding vector. Generally, there may be a plurality of spatial streams that participate in spatial multiplexing, and precoding vectors of these spatial streams correspond to column vectors of the precoding matrix. Related content of the spatial stream, the precoding vector, and the precoding matrix can be found in the prior art, and therefore details are not described in this specification.
In a scenario in which a weighted sum of a plurality of component vectors that match a channel the most is used as a precoding vector, quantity of quantization bit of a weight (i.e., combination coefficient) of one component vector is equal to that of any other component vector. This causes improper overheads when feeding back indication information that indicates a combination coefficient, and therefore makes an overall system performance gain unsatisfactory.